1. Field of the Invention
This invention relates to photopolymerizable elements and relief image printing plates derived therefrom and is more particularly concerned with photopolymerizable elements comprising a polymerizable monomer and a polymerization initiator incorporated in a polyurethane binding agent and with relief image printing plates derived therefrom.
2. Description of the Prior Art
It is known to prepare photopolymerizable elements suitable for the preparation of relief image printing plates by casting or molding into a sheet-like form a mixture of (a) an addition polymerizable monomer having ethylenic unsaturation, (b) a free radical initiator for said monomer which is activatable by light, and (c) a suitable base material which can be one of a wide variety of materials including rubber and synthetic polymers; see Plambeck U.S. Pat. No. 2,760,863. It is also known that polyether-based polyurethanes can be employed as the base material in such compositions; see Barney U.S. Pat. No. 2,948,611. The use has also been reported of polyurethanes, which contain ethylenic unsaturation in the chain thereof and which thereby can be used in place of a polymerizable monomer; see Kurtz U.S. Pat. No. 3,658,531.
We have now found that photopolymerizable elements which have improved properties (to be discussed hereafter), and which give rise to relief image printing plates having improved properties, are obtained by employing certain polyester-based polyurethanes as the base material in the above types of compositions.